Traumatic Brain Injury (TBI) is frequently referred to as a "silent epidemic" because its lasting impairments do not leave visible scars and public awareness has historically been limited. In reality, a TBI marks the beginning of a chronic disease, from which 5.3 million Americans currently suffer persistent symptoms that cause major limitations in daily function and significantly impact quality of life for decades after the injury. Regardless of severity of injury, 76% of TBI survivors have at least one symptom and 53% have at least 3 symptoms at one year post injury. The symptoms seen most frequently post-TBI, and on which this application focuses, are those that influence cognition, behavior, and emotion. These symptoms have a significant impact on employability, quality of life, and family dynamics. It is completely unknown why some patients fully recover and are symptom free, while others who have the same extent of injury, same care, and same demographic factors develop lifelong symptoms. The long-term goal of our research is to identify the biological underpinnings influencing variability in symptomatology post- TBI and to use this information to develop evidence-based interventions that are tailored to an individual's genomic risk profile. Our overall objective of this application is to determine the extent that variability in genes involved in the mitochondrial oxidative phosphorylation (OXPHOS) pathway, responsible for cellular energy production, is responsible for variability in symptoms related to cognition, behavior, and emotion post-TBI. We are focusing on the OXPHOS pathway because availability of cellular energy impacts extent of neurological damage after TBI and our preliminary data shows genetic variability in the mitochondrial genome and efficiency of the OXPHOS pathway impact symptomatology up to 2 years post-TBI. Our data also indicate a possible moderating gender effect on the influence of mitochondrial genotype on both OXPHOS efficiency and symptomatology after TBI. To date all of our work has been with the mitochondrial genome;however the majority of genes involved in the OXPHOS pathway are nuclear in origin. This project will evaluate the nuclear genes involved in the OXPHOS pathway using a tagging SNP, candidate pathway, genetic association, with predictive analysis approach to look at both nuclear and mitochondrial contributions to cognitive, behavioral, and emotional symptomatology post-TBI. This application proposes a logical next step in our line of investigation that is necessary in order to fully understand the impact that genetic variability in the OXPHOS pathway has on symptom variability observed in patients after TBI, progress toward risk prediction that includes objective genetic data, and eventually translate these findings to reduce the incidence and severity of symptoms experienced by survivors of TBI. PUBLIC HEALTH RELEVANCE: Traumatic Brain Injury (TBI) is frequently referred to as a "silent epidemic" because its lasting impairments do not leave visible scars and public awareness has historically been limited. In reality, a TBI marks the beginning of a chronic disease, from which 5.3 million Americans currently suffer persistent symptoms that cause major limitations in daily function and significantly impact quality of life for decades after the injury. It is completely unknown why some patients fully recover and are symptom free, while others who have the same extent of injury, same care, and same demographic factors develop lifelong symptoms. The goal of this application is to investigate the role that genetic variability plays in susceptibility to symptoms after TBI with the hope of eventually translating this information into risk assessment and tailored therapies for TBI survivors to reduce the incidence and severity of symptoms post-TBI.